core: drop txHash from SpentCoinState

It's a key for it, makes no sense storing it as data.

pkg/core/dao.go

@@ -219,7 +219,7 @@ func (dao *dao) GetSpentCoinsOrNew(hash util.Uint256, height uint32) (*SpentCoin
 		if err != storage.ErrKeyNotFound {
 			return nil, err
 		}
-		spent = NewSpentCoinState(hash, height)
+		spent = NewSpentCoinState(height)
 	}
 	return spent, nil
 }

pkg/core/spent_coin_state.go

@@ -3,12 +3,10 @@ package core
 import (
 	"github.com/nspcc-dev/neo-go/pkg/core/transaction"
 	"github.com/nspcc-dev/neo-go/pkg/io"
-	"github.com/nspcc-dev/neo-go/pkg/util"
 )
 
 // SpentCoinState represents the state of a spent coin.
 type SpentCoinState struct {
-	txHash   util.Uint256
 	txHeight uint32
 
 	// A mapping between the index of the prevIndex and block height.
@@ -23,9 +21,8 @@ type spentCoin struct {
 }
 
 // NewSpentCoinState returns a new SpentCoinState object.
-func NewSpentCoinState(hash util.Uint256, height uint32) *SpentCoinState {
+func NewSpentCoinState(height uint32) *SpentCoinState {
 	return &SpentCoinState{
-		txHash:   hash,
 		txHeight: height,
 		items:    make(map[uint16]uint32),
 	}
@@ -33,7 +30,6 @@ func NewSpentCoinState(hash util.Uint256, height uint32) *SpentCoinState {
 
 // DecodeBinary implements Serializable interface.
 func (s *SpentCoinState) DecodeBinary(br *io.BinReader) {
-	br.ReadBytes(s.txHash[:])
 	s.txHeight = br.ReadU32LE()
 
 	s.items = make(map[uint16]uint32)
@@ -51,7 +47,6 @@ func (s *SpentCoinState) DecodeBinary(br *io.BinReader) {
 
 // EncodeBinary implements Serializable interface.
 func (s *SpentCoinState) EncodeBinary(bw *io.BinWriter) {
-	bw.WriteBytes(s.txHash[:])
 	bw.WriteU32LE(s.txHeight)
 	bw.WriteVarUint(uint64(len(s.items)))
 	for k, v := range s.items {

pkg/core/spent_coin_state_test.go

@@ -10,7 +10,6 @@ import (
 
 func TestEncodeDecodeSpentCoinState(t *testing.T) {
 	spent := &SpentCoinState{
-		txHash:   random.Uint256(),
 		txHeight: 1001,
 		items: map[uint16]uint32{
 			1: 3,